As is known in the art, there is a desire to lower acquisition and life cycle costs of radio frequency (RF) systems which utilize phased array antennas (or more simply “phased arrays”). At the same time, bandwidth, polarization diversity and reliability requirements of such systems become increasingly more difficult to meet.
As is also known, one way to reduce costs when fabricating RF systems is to utilize printed wiring boards (PWBs) (also sometimes referred to as printed circuit boards or PCBs) which allow use of so-called “mixed-signal circuits.” Mixed-signal circuits typically refer to any circuit having two or more different types of circuits on the same circuit board (e.g. both analog and digital circuits integrated on a single circuit board).
As is also known, RF circuits are often provided from multi-layer PWBS. Such PWBS are often made from polytetrafluoroethene (PTFE) based materials since such materials have favorable RF characteristics (e.g. favorable insertion loss characteristics).
Mixed signal multilayer PWB laminates and often provided from sub-assemblies with each sub-assembly arranged for different types of circuits. For example, one sub-assembly may be for RF circuits and other sub-assembly for D.C. power and logic circuits. The two sub-assemblies are combined to provide the mixed signal, multi-layer PWB. Such PWBS are typically provided from PTFE based materials and thus require multiple process step-cycles for each sub-assembly which makes up the mixed signal multi-layer PWB. For example, it is necessary to image and etch the desired circuits the specified layers, then laminate the boards to provide a multilayer PWB. The drill and plate operations are sometime performed on individual boards. Finally, a last laminate and drill and plate cycle is performed to provide a finished PWB sub-assembly or final PWB assembly. Typically, each PWB sub-assembly and/or final assembly requires that each RF via hole extending beyond the transmission line junction (such regions referred to as “via stubs”) be back-drilled and back-filled. This step improves RF performance of the PWB but increases cost and degrades RF performance due to back-drill tolerances, back-fill material dielectric properties and trapped air pockets. Thus, this approach results in high cost RF multilayer PWB laminates due to multiple fabrication operations and back-drill/backfill operations.
Mixed signal multilayer PWBs provided using low temperature co-fired ceramic (LTCC) based materials (rather than PTFE-based materials) present a different set of fabrication problems. Although a multilayer laminate can typically be made in one lamination step using LTCC, LTCC has a number of drawbacks. For example, processing can only be done on relatively small panel (or board) sizes (typically 6″ square or less) due to shrinkage issues. Also, LTCC based materials use a conductive paste for transmission lines and ground planes and such conductive paste is lossy at RF frequencies compared to losses in RF signals propagating through pure copper transmission lines used in PTFE boards. Such increased insertion loss is unacceptable at many frequency ranges (e.g. at Ku-Band and above). Furthermore, LTCC materials tend to have a dielectric constant which is higher than the dielectric constant of PTFE based boards and this may not be suitable for both RF transmission lines and efficient RF radiators. Lastly, LTCC has a relatively small manufacturing base. In summary, at the present time, LTCC does not have high volume capability and LTCC material compromises RF performance and severely limits applications above the L-Band frequency range. Thus, both PTFE and LTCC approaches result in circuits which are relatively expensive, degrade RF performance and limit radar and/or communications applications.
As is known in the art, a phased array antenna includes a plurality of antenna elements spaced apart from each other by known distances coupled through a plurality of phase shifter circuits to either or both of a transmitter or receiver. In some cases, the phase shifter circuits are considered to be part of the transmitter and/or receiver.
As is also known, phased array antenna systems are adapted to produce a beam of radio frequency energy (RF) and direct such beam along a selected direction by controlling the phase (via the phase shifter circuitry) of the RF energy passing between the transmitter or receiver and the array of antenna elements. In an electronically scanned phased array, the phase of the phase shifter circuits (and thus the beam direction) is selected by sending a control signal (e.g. a series of digital bits or a digital control word) to each of the phase shifter sections. The control word is typically a digital signal representative of a desired phase shift, as well as a desired attenuation level and other control data.
Including phase shifter circuits and amplitude control circuits in a phased array antenna typically results in the antenna being relatively large, heavy and expensive. Size, weight and cost issues in phased array antennas are further exacerbated when the antenna is provided as a so-called “active aperture” (or more simply “active”) phased array antenna since an active aperture antenna includes both transmit and receive circuits.
Phased array antennas are often used in both defense and commercial electronic systems. For example, Active Electronically Scanned Arrays (AESAs) are in demand for a wide range of defense and commercial electronic systems such as radar surveillance, terrestrial and satellite communications, mobile telephony, navigation, identification, and electronic counter measures. Such systems are often used in radar for National Missile Defense, Theater Missile Defense, Ship Self-Defense and Area Defense, ship and airborne radar systems and satellite communications systems. Thus, the systems are often deployed on a single structure such as a ship, aircraft, missile system, missile platform, satellite or building where a limited amount of space is available.
AESAs offer numerous performance benefits over passive scanned arrays as well as mechanically steered apertures. However, the costs that can be associated with deploying AESAs can limit their use to specialized military systems. An order of magnitude reduction in array cost could enable widespread AESA insertion into military and commercial systems for radar, communication, and electronic warfare (EW) applications. The performance and reliability benefits of AESA architectures could extend to a variety of platforms, including ships, aircraft, satellites, missiles, and submarines.
Many conventional phased array antennas use a so-called “brick” type architecture. In a brick architecture, radio frequency (RF) signals and power signals fed to active components in the phased array are generally distributed in a plane that is perpendicular to a plane coincident with (or defined by) the antenna aperture. The orthogonal arrangement of antenna aperture and RF signals of brick-type architecture can sometimes limit the antenna to a single polarization configuration. In addition, brick-type architectures can result in antennas that are quite large and heavy, thus making difficult transportability and deployment of such antennas.
Another architecture for phased array antennas is the so-called “panel” or “tile” architecture. With a tile architecture, the RF circuitry and signals are distributed in a plane that is parallel to a plane defined by the antenna aperture. The tile architecture uses basic building blocks in the form of “tiles” wherein each tile can be formed of a multi-layer printed circuit board structure including antenna elements and its associated RF circuitry encompassed in an assembly, and wherein each antenna tile can operate by itself as a substantially planar phased array or as a sub-array of a much larger array antenna.
For an illustrative phased array having a tile architecture, each tile can be a highly integrated assembly that incorporates a radiator, a transmit/receive (T/R) channel, RF and power manifolds and control circuitry, all of which can be combined into a low cost light-weight assembly for implementing AESA. Such an architecture can be particularly advantageous for applications where reduced weight and size of the antenna are important to perform the intended mission (e.g., airborne or space applications) or to transport and deploy a tactical antenna at a desired location.
It would, therefore, be desirable to provide an AESA having an order of magnitude reduction in the size, weight, and cost of a front end active array as compared to existing technology, while simultaneously demonstrating high performance.